The present invention relates generally to optical semiconductor devices and is particularly advantageous for optical semiconductor devices operable in wavelengths above 1.3 xcexcm.
Over the past few decades, the field of optics has been used to enhance high-speed data communications in wide-ranging technology areas including, among a variety of others, laser printers, data storage, and optical telecommunications. In connection with optical telecommunications, for example, this development has largely displaced the large conical horn-reflector tower-mounted radio antennas having underground optical cables for telecommunication trunks to carry information traffic in the form of optical signals. Currently, quartz glass optical fibers are used to carry high volumes of data generated as light pulses at one end by laser diodes and detected at the other end by optical detectors.
A multi-heterojunction laser diode grown on a GaAs substrate is one common semiconductor device used as an optical transmitter for telecommunications applications. However, the relatively short wavelength of conventional GaAs devices (e.g., 820 nm) limits performance due to the wavelength dependent dispersion and loss properties of optical fiber. Additionally, the short wavelength limits the permissible optical power because of eye safety considerations. Longer optical wavelengths can overcome many of these limitations and allow data transmission at higher rates over longer distances. Efforts to improve long wavelength devices have included altering the various interfaces and internal compositions of each layer to tune the devices for minimum cost of fabrication, optimal device performance, and reductions in terms of size, heat generation and power consumption.
The wavelengths desired for laser sources in telecommunications are those for which the optical fiber has the lowest dispersion, 1.3 xcexcm, or minimum loss, 1.55 xcexcm. Thus, there have been ongoing efforts to produce improved optical semiconductor devices that operate at these wavelengths. There is no binary semiconductor with a bandgap at these wavelengths. Therefore, the focus has been to develop GaAs-based ternary or quaternary structures to achieve materials with bandgaps suitable for long wavelength devices.
The longest wavelengths available for devices on GaAs substrates have been typically around 1 xcexcm and realized using single or multiple-layer InGaAs quantum wells. Growing InGaAs quantum wells on GaAs with optical wavelengths beyond 1.1 xcexcm is difficult because increasing indium content further leads to the formation of crystalline defects and mechanical tension, compression or shear in and around the active layer. This internal stress can be attributable to, among other factors, lattice mismatch between the active region and the substrate, and improper temperature control during manufacture of the laser diode device. Inadequate temperature control during manufacture can also result in a higher threshold current of laser oscillation and poor temperature characteristics.
The addition of more indium to the InGaAs quantum well material, in an attempt to achieve longer wavelengths, is a limited approach because both the strain energy and the quantum confinement energy increase with increasing indium content. The quantum confinement energy increases because increasing indium results in smaller effective masses and deeper quantum wells which both serve to push the first quantum confined level to higher energies. Much of the decrease in the bulk energy gap associated with increasing the indium content of the quantum well material is negated, and more indium is required to achieve a given wavelength than would be predicted by the bulk bandgap dependence on the indium mole fraction.
Use of ternary materials, such as GaInAs, produces compressively strained structures when grown on GaAs substrates. Addition of a fourth small atom can be used to decrease the size of the lattice and reduce the mechanical strain of the structure. The addition of nitrogen to the laser diode active region composed of InGaAs can result in the longest wavelengths devices achievable on GaAs substrates. The nitrogen causes the bulk bandgap to significantly decrease and second, the associated smaller lattice constant of GaN results in less strain in GaInNAs compared to InGaAs without the nitrogen.
In a device that incorporates N in the active layer, several layers are included at the device center in active region of GaInNAs. This active region is used as the main source for the generation of light pulses, and includes outer GaAs contact layers grown on a GaAs substrate. To the inside of the outer contact layers and immediately bordering either side of the active layer are upper and lower cladding regions to contain core light while protecting against surface contaminant scattering. In response to a voltage differential presented via the electrodes at the outer contact layers, holes and electrons are respectively injected into the active layer from the layers above and below. The accumulation of these holes and electrons within the active layer results in their recombination, thereby stimulating the emission of photons and, oscillation at a wavelength defined largely by the composition of the active layer. Lasers operating at wavelengths beyond 1.3 xcexcm have been demonstrated with InGaNAs active regions grown on GaAs substrates. Further, GaInNAs vertical cavity surface emitting laser (VCSEL) devices have been implemented.
Growing high quality GaInNAs material suitable for use in optical devices with wavelengths beyond 1.3 xcexcm continues to be challenging. Compositions of GaInNAs that emit light significantly beyond 1.3 xcexcm have thus far been impractical for use in optical devices due to high threshold currents.
The present invention is directed to an approach for improving the photoluminescent output of an optical-electronic semiconductor device at wavelengths longer than 1.3 xcexcm through the incorporation of antimony into the active region of the device. Various example embodiments of the present invention are directed to and are advantageously used in many high-speed data communication applications, such as in the above-listed technology areas.
In accordance with one embodiment of the present invention, an optica-electronic semiconductor device includes a GaAs-based substrate and an active region over the GaAs-based substrate. The active region includes a GaInNAsSb-based quantum well layer adjacent a GaNAs-based barrier layer
In another embodiment of the invention, an optical-electronic semiconductor device includes a GaAs-based substrate and an active region over the GaAs-based substrate. The active region includes a GaInNAsSb-based quantum well layer adjacent a GaNAs-based barrier layer and including crystal-defect causing impurities. The active region is annealed to remove point defects otherwise present in the active region. Portions of the optical-electronic semiconductor device are electrically coupled to the active region and are adapted for exciting the active region.
In yet another embodiment of the invention, a vertical cavity surface emitting optical-electronic semiconductor device includes a GaAs-based substrate, a first DBR region over the GaAs-based substrate and an active region over the first DBR region, the active region including a GaInNAsSb quantum well layer adjacent a GaNAs barrier layer and including crystal-defect causing impurities. The active region is annealed to remove point defects otherwise present in the active region. The device further includes a second DBR region over the annealed active region. The first and second DBR regions are oppositely-doped and oppositely-doped electrodes electrically coupled to the correspondingly respective first and second DBR regions, are adapted for exciting the active region and causing emissions through the GaAs-based substrate.
In another embodiment of the invention, an edge-emitting optical-electronic semiconductor device includes a GaAs-based substrate and an active region over the GaAs-based substrate. The active region includes multiple GaInNAsSb-based quantum well layers, each being surrounded by a pair of adjacent GaNAs-based barrier layers. The device further includes a first and a second cladding portion electrically coupled to the quantum well active region and adapted for exciting the active region.
Another embodiment of the invention includes a method for manufacturing an optical-electronic semiconductor device. The method includes providing a GaAs-based substrate and forming an active region over the GaAs-based substrate. The active region includes a GaInNAsSb-based quantum well layer adjacent a GaNAs-based barrier layer. The method further includes forming portions electrically coupled to the active region and adapted for exciting the active region.
In another embodiment of the invention, a method for manufacturing an optical-electronic semiconductor device includes providing a GaAs-based substrate and forming an active region over the GaAs-based substrate. The active region includes a GaInNAsSb-based quantum well layer adjacent a GaNAs-based barrier layer. The method further includes growing a layer over the active region while annealing the active region and providing portions of the optical-electronic semiconductor device electrically coupled to the active region and adapted for exciting the active region.
Another embodiment of the invention is directed to a method for manufacturing a VSCEL optical-electronic device including providing a GaAs-based substrate and forming a multiple quantum well active region over the GaAs-based substrate. The active region includes multiple GaInNAsSb-based quantum well layers, each being surrounded by a pair of adjacent GaNAs-based barrier layers. The method also includes forming mirror portions on either side of the multiple quantum well active region adapted for exciting the active region.
In yet another embodiment of the invention, a method for manufacturing an edge-emitter optical-electronic semiconductor device includes providing a GaAs-based substrate and forming a multiple quantum well active region over the GaAs-based substrate. The active region includes multiple GaInNAsSb-based quantum well layers, each being surrounded by a pair of adjacent GaNAs-based barrier layers. The method includes forming cladding portions electrically coupled to the quantum well active region and adapted for exciting the active region.
The above summary of the present invention is not intended to describe each embodiment or every implementation of the present invention. Advantages and attainments, together with a more complete understanding of the invention, will become apparent and appreciated by referring to the following detailed description and claims taken in conjunction with the accompanying drawings.